1. Field of the Invention
The present invention relates to a fastener driving tool for driving a fastener such as a nail into an object member by employing compressed air or combustion gas, and more particularly, relates to an art of preventing the fastener from unexpectedly dropping from an injection passage, in the fastener driving tool which is so constructed that the injection passage for injecting the fastener is used also as a passage for exhaust air.
2. Background Art
A first example of a conventional fastener driving tool will be described referring to FIG. 6.
FIG. 6 shows a structure around an injection hole 8 of a fastener driving tool which is driven by compressed air. Other parts than the parts which are shown in FIG. 6 have essentially the same structure as in the fastener driving tool according to an embodiment of the invention as shown in FIGS. 1 to 5.
On a slide face 6a of a nose 6 for guiding a driver blade 4, there is formed an exhaust port 7 through which a piston (not shown) is communicated with an injection hole 8 when the driver blade 4 is positioned at a top dead center. After a nail 5 has been driven into an object member (not shown) by means of the driver blade 4 which is provided continuously from the non-shown piston, the compressed air which has been accumulated in a return chamber (not shown) will be supplied to an area below the non-shown piston, and will push the piston upward, thereby to lift the driver blade 4 up to the top dead center, as shown in FIG. 6. On this occasion, the compressed air existing below the non-shown piston is communicated with the injection hole 8 through the exhaust port 7. The compressed air will be discharged to the injection hole 8 through the exhaust port 7, and exhausted to the atmosphere through a gap between the nail 5 and the injection hole 8. At this moment, a stream of the compressed air will push a nail head 5b downward.
Meanwhile, a nail feeder 31 pushes the nail 5 toward the injection hole 8 by means of a spring which is not shown. In case where a plurality of the nails 5 are coupled together, the nails 5 except the nail 5a which is present inside the injection hole 8 are engaged with a guide groove 11, as shown in FIGS. 1 and 5, whereby downward movements of the nails 5 are restricted. Because the nail 5a is coupled to the nails 5, the nail 5a will not fall downward, unless it is driven by the driver blade 4.
When only one nail 5 is left, the nail 5a inside the injection hole 8 is held by being pushed by the nail feeder 31 so as to be butted against the injection hole 8. Engagement between the nail 5 and the guide groove 11 no longer exists, and holding force of the nail 5a will be decreased. It sometimes happens that the stream of the compressed air pushes the nail head 5b at this moment, thereby to release the nail 5a, and the nail 5a drops from the injection hole 8 unexpectedly.
A second example of the conventional fastener driving tool will be described referring to FIG. 7.
FIG. 7 shows a sectional side view of a fastener driving tool 1, as disclosed in Patent Document 1, which is described below, for driving a plurality of nails 5 which are coupled together by means of a plastic sheet. The fastener driving tool 1 is provided with a sheet discharge port 27 for discharging the plastic sheet to the exterior, at a side of supplying the nails 5 in the injection hole 8. The sheet discharge port 27 is provided at a position closer to the injection hole 8 than the nail head 5b. During driving operation of the nail 5, a part of surplus compressed air, after the piston 3 has returned to the top dead center, will be exhausted from this sheet discharge port 27 to the exterior.
[Patent Document 1]
Japanese Patent Publication No. JP-A-2001-198849
(Application No. 2000-14766)
In either of the above described structures, it has sometimes happened that the stream of the compressed air pushes the nail 5a downward, and the nail 5a unexpectedly drops from the injection hole 8, because the holding force is decreased when only one nail 5 is left.